Generator



y PatentedY June 26, 1945 2,378,894 GENERATOR J ohn E. Blankenbuehler,Edgewood. Pa., assignor to Westinghouse Electric Corporation, EastPittsburgh, Pa., a corporation of Pennsylvania Application `July 24,1943, Serial No. l195,980

(Cl. P11-228) 6 Claims.

My invention relates generally to generators, and it has reference inparticular to arc welding generators of the cross-eld type.

Generally stated, it is an object of my invention to provide in a simpleand inexpensive manner for improving the arc welding characteristics ofcross-iield generators.

More specifically, it is an object of my invention to provide forincreasing the open circuit arc striking voltage of arc weldinggenerators of the cross-field type without causing-undesirablecommutating conditions at the auxiliary brushes.

It is also an object of my invention t provide for improving thecommutating characteristics at the auxiliary brushes in a generator ofthe crossiieici type.

Another object of my invention is to provide a simple method ofincreasing the open circuit voltage of existing generators of thecross-field type by providing suillcient auxiliary excitation ci thefield windings to increase the no-load circulating current in theauxiliary brush circuit, and utilizing a commutating pole positioned atthe point oi maximum amature potential relative to the main brushes forpreventing undesirable commutation at the auxiliary brushes.

Yet another object of my invention is tc provide increased auxiliaryexcitation of a iield pole winding in a generator of the cross-ileldtype and connect a commutating pole winding in the auxu iliary brushcircuit to neutralize .the eiect o: the increased excitation on thecommutation at the auxiliary brushes.

Other objects will in part be obvious, and will in part be explainedhereinafter. i

In practicing my invention in onev form thereof, the auxiliaryexcitation usually applied to the series iield windings of generators ofthe crossiield type for determining the polarity of the main loadbrushes is increased suifioiently to in crease the open circuit voltageavailable at the main brushes, tor the purpose of improving the areetiilauiv: characteristics' of the generator. A oommutatiugpole ispositioned to one side or the armature ,substantially intermediate thevmain nel@ polo meinimrc and is provided with a commutatine windingconnected in series circuit re lation with the auxiliary brushes forneutralizing the otherwise harmful eiects or the increased auxiliaryexcitation ouJ commutation at the auxiliary brushes. l

For a more complete understanding of the nature and scope .ci mymventiomreferenee may be had to the following detailed description which`weil known may be read in connection with the drawing, in which:

Figure 1 is a diagrammatic view of an arc welding system embodying theprincipal features of the invention; and

Fig. 2 represents load characteristic curves of a cross-Held generatorbefore and after embodying features of the invention.

Referring to Figure 1, the reference numeral' lli may denote generallyan arc welding generator of the cross-eld type which is arranged forsupplying welding current to an electrode ll for performing a weldingoperation on work I2.

The generator Ill may comprise, generally a frame I3 of magneticmaterial having eld pole members l5 and i6 positioned therein in opposedrelation. The field p'ole members comprise body portions I8 and I9,respectively, which are positioned adjacent the frame i3 and surroundedby series field windings 20 and 2|. The body members IB and I9 arepreferablyV of a relatively small cross-section, so that they saturateat the values of welding current well below the normal range of weldingcurrent.

The eld p ole members may also be provided with enlarged arcuate shoeportions 23 and 24, respectively, having recessed central portions 26and 21 with central projections 28 and 29, respectively, foraccommodating compensating windings 3l and 32 in a manner well known inthe art. Means. such as the supports 34, may be provided between thearcuate shoe portions and the frame adjacent the ends of the shoeportions to provide a more rigid mechanical structure. These supportsare preferably of a non-magnetic materia-i, such as brass.

The generator may be provided in the usual manner with an armature 3Bpositioned intermediate the arcuate shoe portions oi the field polemembers. Auxiliary brushes 3o may be provided for they armature, beingpositioned along en axis substantially perpendicular to 'the axis of theeld pole members Main brushes 3S may be positioned substantially alongthe oi the @leid pcie members and connected in series circuit relationwith the series held windings Eil and the compensating windings 3i andci., elec trede i i and work t2,

Suitable means may be provided in a manner in the art for controllingthe output ci the generator such. as, ior example., the magnetic shuntmember 40 which may be supported adjacent'the tips of the arcuate shoemembers 23 and It and to one side of the armature 36 by support platesIl which4 may be secured to the polarity of the generator ill,I suitableauxiliary excitation may be providedv for either one or both of theiield polewindings 2l and 2|, or an additional eld winding connected toa source of auxiliary excitation may be provided in a manner well knownin the art for maintaining the residual polarity of the field polemembers in a predetermined direction. For example, a source ofunidirectional current may be provided by connecting a rectifier bridgecircuit 42 to a suitable source of alternating current 43 and utilizinga reversing switch 44, together with conductors and 4E, to connect theunidirectional source across the series field windings Zland 2i and thecompensating windings 3| and 32.

In order to provide for increasing the normal open circuit voltageavailable at the electrode ii for striking an arc on the work i2, theamount of auxiliary excitation produced by the auxiliary source 4| maybe increased to a value in excess of the usual polarity controlexcitation. In one instance, for example, with a cross-field generatorof the type illustrated, I have found that, by increasing the voltageavailable at the auxiliary source 4I sui'ilciently` to increase theauxiliary excitation of the series i'ield windings 2li and 2i at no-loadfrom approximately l to 16 amperes, it is possible to increase the opencircuit voltage of the generator from 45 to 60 volts. This greatlyimproves the arc strikingcharacteristics of the generator and improvesthe quality of the welds produced. With an increase of the auxiliaryexcitation, the residual or no-load magnetic flux in the body portionsof the field pole members I5 and i6 is increased correspondingly.Accordingly, the circulating current which flows in the auxiliary brushcircuit due to the armature conductors cutting the residual magneticflux when the generator is running at no-load, will be increasedsubstantially in proportion. This increase of current in the auxiliarybrush circuit creates an undesirable commutation condition at theauxiliary brushes resulting in arcing of the brushes.

In order to improvecommutation atv the 'auxiliary brushes, and toneutralize or compensate for the increased current in the auxiliarybrush circuit, a commutating pole Il may be positioned to one side ofthe armature 36, substantially in-v termediate the field pole members i5and I B. A winding 49 may be positioned on the commutating pole 48 andconnected in series circuit relation with the normally short-circuitedauxiliary brushes 38. By providing the winding 48 with a number'of turnsapproximately equal to 'two and one-half times the number "of armatureturns which are effective to produce a magnetic flux opposing that ofthe commutating pole 4I, I have found that highly satisfactory operationof the generator may be secured even with the increased current in theauxiliary brush circuit.

It will be noted that the ratio of commutating field pole turns toopposing armature turns is 4substantially greater in the case of across-iieldl generator than with generators of the usual type where itis common to operate with only one and one-quarter times the number ofturns opposing amature turns on the commutating pole.

Since the cross-field type of generator is inclined to be relativelycritical as to commutation even where the no-load voltage is notincreased, and where polarity control excitation is not used, acommutating pole may be used to advantage in accordance with myinvention. A symmetry of the air gap or misalignment of the field polemembers, which usually result in substantial increases of no-loadauxiliary brush current. can readily be neutralized by the use of acommutating pole which may be positioned intermediate the main iieldpole members on one side of the armature where a single magnetic shuntis used on the other side oi' the armature. lower grades of brushes maybe used with a oommutating pole, whether or not the current isincreased, thereby aifording an appreciable saving.

Referring to Fig.' 2, the letter a designates a typical loadcharacteristic or volt-ampere curve of a 30D-ampere arc weldinggenerator of the cross-field type embodying the features of theinvention. The dotted curve b represents a typi- A cal loadcharacteristic or volt-ampere curve of the same generator beforeembodying the features of my invention. It will be, noted that the opencircuit voltage of the generator has been increased from 45 to 60 volts,thereby greatly in'iproving the arc striking characteristics lof thegenerator.

Since the curves a and b merge at the point c where saturation of thebody portions of the field.

pole members effectively determines the load characteristic curve, theload characteristics oi' a cross-iield generator embodying the featuresoi the invention are not affected within the normal operating range ofthe generator.

The curves d and e represent variations in-the auxiliary lbrush circuitcurrent corresponding to the different values of load current.Thoughlthe auxiliary brush current at no-load is increased tainedwithout material alteration of the generator and at a minimum of expenseand labor. Such an improvement is relatively important when it isconsidered that, in order to obtain the same results by redesign of themachine itself, the number of armature tunis, the size of the armature,the amount of iron therein, and also the-overall size of the machinewould have to be greatly increased to obtain the same results. Under thepresent conditions, when copper and iron are vital materials, it will berealized that the invention is a valuable aid to the conservation ofthese materials, as well as an important improvement tofthe weldinggenerator, and a valuable contribution to the arc welding industry.

Since different embodiments of the invention may be made and certainchanges may be made in the drawing and description without departingfrom the spirit and scope of the invention, it is intended that all thematter contained in tho In addition,'

abovedescription or shown in the accompanying drawing shall be construedas illustrative and not in a limiting sense.

I claim as my invention: g

1. A generator comprising, a frame structure, an armature rotatablymounted in the frame structure and provided with main and auxiliaryclose-circuited brushes, a pair of field pole members supported by theframe structure havingv excitation windings thereon, circuit meansproviding sufficient auxiliary excitation to one of the said excitationwindings to substantially increase the open circuit voltage of the mainbrushes, and an interpole structure positioned intermediate the tleldpole members on one side of the armature having a winding thereonconnected between the auxiliary circuit brushes.

2. A cross-iield generator comprising, a pair of opposed iield polemembers having excitation windings thereon, an. armature rotatablypositioned between the eld pole members having main and auxiliarybrushes, circuit means connecting at least one Aof the field poleexcitation windings to a separate source of excitation, and

yan interpole structure positioned intermediate the iield pole membershaving a commutating winding thereon connected in series relation withthe auxiliary brushes to compensate for the auxiliary brush commutationconditions caused by i series circuit relation to the auxiliary brushes.

4. A generator comprising, an amature having a commutator with pairs ofmain and auxiliary ing a pair of iield pole members on opposite sides o!the amature having windings connected in series circuit relation withthe main brushes. and a commutating field pole member positionedsubstantially along the axis of the auxiliary brushes having a windingconnected in series circuit relation with the auxiliary brushes.

5. An arc welding generator having an armature with main and auxiliarybrushes, a pair o! field pole members having excitation 4windingsconnected in series with the main brushes, circuit means connecting thefield pole windings to a source of auxiliary excitation of sufilcientvoltage to raise the open circuit voltage of the main brushes, and acommutating pole positioned on one side of the armature substantiallyiliary brushes positioned along axes electrical degrees apart, a framehaving opposed main neld pole members with ileld windings thereon connected in series circuit relation with the main brushes, means includinga reversing switch for applying sumcient auxiliary excitation to one oflthe eld windings to increase the residual ilux in the main field polelmembers whereby'the noload circulating current in the auxiliary brushcircuit is increased suiilciently to produce the desired open circuitvoltage, and means including a commutating iield pole memberintermediate the main iield pole members having a commutating windingthereon connected in series circuit relation with the auxiliary armaturebrushes to correct undesirable commutation conditions produced by theeffects of-the auxiliary excitation at no load. y

JOHN H. BLANKEN'BUEHLER.

